The most serious defect of the piano is its inability to sustain its tones. The tones of the voice and of wind instruments are limited in duration only by the air capacity of the lungs, those of bowed string instruments can be held indefinitely, and an organ pipe will sound as long as the air pressure is maintained in the bellows. The vibrations of a piano string, on the contrary, are at their maximum only during the moment in which it is struck by the hammer operated by pressing the key, and from that moment gradually decrease, giving forth a sound constantly fainter and fainter. Once the key is struck, the player's control over the mechanism ceases, and he has no choice but either to wait passively for silence or to strike another key. For this reason the broad, poising melodies and the slow-moving, deliberate harmonies of the choral and organ schools are ineffective on the piano. The long notes, fading momently away, fail, because of the insufficiency of their physical embodiment, to receive their due share of attention, and so lose their musical value. Still more do purely polyphonic passages, which depend for their effect on the leisurely succession of dissonances and their resolutions, subtly interlinked, suffer from the discontinuity of the piano tone. The indifference, or even insensibility, to the beauty of pure line, which characterizes so much of our modern musical taste, is probably in large measure due to the prevalence of an instrument so little suited to exhibit it.[20]
At a very early period after the piano came into common use, musicians began to recognize the necessity of minimizing its characteristic defect by modifying their manner of writing. They soon discovered that if the tones would not sustain themselves, they must be struck over and over again as rapidly as possible: repetition must counteract evanescence. An early application of this principle is the use, by Bach and other clavichordists, of trills, mordants, and other ornaments as a means of keeping long melody-notes audible. A more important one is the breaking up of chords into figures of short notes in the accompaniments of Haydn and Mozart, a device which soon became so indispensable that a glance at any modern piano score will discover hundreds of such groups of short notes, which are nothing but chords played piecemeal in order to make them sound.